Summary
Cross-Origin-Opener-Policy header is a response header that allows a site to control if others included documents share the same browsing context. Sharing the same browsing context with untrusted documents might lead to data leak.
Solution
Ensure that the application/web server sets the Cross-Origin-Opener-Policy header appropriately, and that it sets the Cross-Origin-Opener-Policy header to 'same-origin' for documents. 'same-origin-allow-popups' is considered as less secured and should be avoided. If possible, ensure that the end user uses a standards-compliant and modern web browser that supports the Cross-Origin-Opener-Policy header (https://caniuse.com/mdn-http_headers_cross-origin-opener-policy).
References
Code
org/zaproxy/zap/extension/pscanrulesAlpha/SiteIsolationScanRule.java